The control mechanisms of IgE production are under study utilizing a mouse model system. Currently the emphasis is on two types of approaches: first, genetic experiments to better understand the control of specific IgE production. Several mouse strains have been found that lack the ability to produce IgE after an antigenic challenge; breeding experiments are attempting to determine whether the genetic defects in these negative strains are identical. These strains are also being crossed to "normal" IgE producing strains to better understand the genetic controls. The second approach is an attempt to purify murine IgE and develop a radioimmunoassay capable of quantitating the small amounts of IgE present in mouse serum (estimated to be less than 1.0 microgram/ml).